The incident beam must be specified for scattering simulations with 2D detector (SAS and GISAS). For other simulations, the beam is set internally according to the given scan model.
To create a beam, use
beam = ba.Beam(intensity, wavelength, alpha, phi=0)
For the wavelenth, use unit multiplier *nm or *angstrom.
For the glancing angle $\alpha_\text{i}$, use unit multiplier *deg.
The azimuthal angle $\varphi_\text{i}$ can be omitted,
as in most applications the default value 0 is pertinent.
After creation of a beam, properties can be set with
beam.setIntensity(intensity)
beam.setFootprintFactor(footprint)
beam.setPolarization(polarization)
For the arguments, see footprint and polarization.
The beam intensity may appear inconsequential for specular simulations because resulting reflectivities are normalized. However, the intensity does influence the simulated noise.